Police in the Kenyan capital, Nairobi, have shot and killed 21 people in a gun battle with suspected members of the banned Mungiki sect.
Recent grisly murders blamed on the Mungiki have shocked Kenyans
Police say their officers engaged "a gang of thugs" resisting an operation to recover firearms stolen from three policemen who were killed on Monday.
Several weapons are said to have been recovered and some policemen injured.
Last week, the president warned Mungiki activities would no longer be tolerated and ordered a shoot-to-kill policy.
The security forces in Kenya have spent the past three months trying to crack down on criminal elements in the Mungiki - a sect which it is claimed runs an extensive extortion operation and is reported to have connections high up in Kenya politics.
The police have blamed them for the beheading of six people last month in central Kenya.
Police spokesman Eric Kiraithe said the morning shoot-out took place in the Mathare district of Nairobi - a run-down industrial sector.
KENYA'S SECRETIVE MUNGIKI
Banned in 2002
Thought to be ethnic Kikuyu militants
Mungiki means multitude in Kikuyu
Inspired by the Mau Mau rebellion of the 1950s
Claim to have more than 1m followers
Promote female circumcision and oath-taking
Believed to be linked to high-profile politicians
Control public transport routes, demanding levies
Blamed for revenge murders in the central region
He said police have cordoned off a large area of the slum reputed to host criminal gangs in the city.
"Security officers during the operation met with resistance from a crowd of armed people who fired at the officers leading to the shoot-out and most of them were killed," Mr Kiraithe told the BBC News website.
Three pistols, machetes and other crude weapons were recovered from the slain suspects and from several houses that were ransacked by the police's feared paramilitary wing, he said.
On Monday night, three police officers were killed while on patrol on foot in the Mathare slums. They were robbed of their AK-47 rifles.
The Mungiki are thought to be militants from Kenya's biggest ethnic group, the Kikuyu.
Last week, President Mwai Kibaki reacted angrily to a spate of recent grisly murders and beheadings in the central region blamed on the Mungiki.
They are said to have been revenge attacks on people who had leaked information about their activities to the police.
"There is no-one who has the right to take a life and if you choose to do that and try to hide we will get you," Mr Kibaki said.
The Mungiki, which means multitude in Kikuyu, claim to have more than one million followers across the country.
Some commentators have linked them to politicians wanting to cause unrest and fear ahead of December elections.
The sect promotes female circumcision and oath-taking and was outlawed in 2002.
In recent years they have been battling with public transport operators who refuse to pay them protection fees.